Electric cable and method of manufacture



Jun 16, 9 J. J. MORRISON ELECTRIC CABLE AND METHOD OF MANUFACTURE Filed Sept. 24, 1940 I I E- 1- I 05 2 Corie/4 EUU/Vfi 5%.510 J (OP/DEE (O/VDUCTOE f7 009 (onse m fieou/va Kama/c7025 l0 (PEPE P4254? I? /mvs/Q Patented June 16, 1942 ELECTRIC CABLE AND METHOD OF MANUFACTURE James J. Morrison, Worcester, Mass, assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey Application September 24, 1940, Serial No. 358,159

7 Claims.

This invention relates to an improved flexible type of portable electric cable and to the method of manufacturing the same. The outstanding feature of novelty resides in the provision of a power cable for the transmission of electric current, comprising a plurality of insulated conductors enclosed within a body of moldable or extrudab-le insulating material such as rubber or the like, with a sheath of fibrous elastic material interposed between the insulated conductors and the moldable insulating material, which fibrous material is characterized by an inherent ability to stretch an appreciable extent so that it may be forced without rupture into the interstices or valleys between the conductors, upon vulcanization or other heat treatment of the moldable insulating material enveloping the assemblage.

An object of the invention is to provide an improved power cable and method of manufacture which will result in the production of a cable adapted to be repeatedly flexed and subjected to torsional stresses without damaging the insulation of the individual conductors of the cable.

In carrying out the invention, I assemble a plurality of insulated conductors in juxtaposition to one another by any conventional cabling operation. I then apply to the assemblage a wrapping of crepe material such as crepe paper, which is characterized by a considerable inherent elasticity or ability to stretch an appreciable extent without rupture. Such an assemblage is then covered with a body of rubber either by an extrusion operation, a molding operation, or other conventional method of enveloping conductors. Thereupon the rubber body is vulcanized. Upon vulcanization, the mass of rubber expands inwardly, thus stretching the crepe material and pressing it into the valleys between the adjacent assembled conductors. The sheath of crepe paper or its equivalent forms a nonadherent sheath which is interposed between the insulated conductors and the body of insulation and in effect constitutes a slip belt. The use of crepe material such as crepe paper or its equivalent in this environment is of imoortance since the corrugated texture of such crepe material for a given weight per unit of length of tape provides considerably more bulk or volume than that of fabric tape, plain paper, kraft paper, varnished cambric, or other fibrous or textile wrapping materials heretofore used.

The present invention, while not limited thereto, is well suited for use in cables of the type having metallic shielding and particularly so where ground conductors are incorporated in the cable in electrical contact with such shielding,

The invention will be fully apparent from the following detailed disclosure and the appended claims when read in connection with the accompanying drawing.

In the drawing, Figure 1 is an elevation with portions broken away to reveal the interior structure of the cable.

Figure 2 is a cross-sectional view showing a plurality of conductors assembled in juxtaposition and surrounded with a sheath of elastic material such as crepe paper or its equivalent.

Figure 3 is a cross-sectional view on line III-III of Figure 1, through a completed cable made in accordance with, and embodying features of, the present invention.

Figure 4 is a detail view of a length of crepe material.

Referring in detail to the drawing, the numeral 2 indicates conductor usually composed of stranded copper wires; Each conductor 2 is provided with a layer of insulation 4, and the several conductors are cabled together so as to lie in juxtaposition either parallel to one another or helically intertwisted. The insulation 4 surrounding each conductor may be of a conventional rubber-like material, varnished cambric, paper, or other materials commonly used in the art. trated, over the insulation 4 of each conductor there is provided a cover 6 of woven or braided fibrous material. This cover 6 may, if desired, be colored so as to provide for identification. Surrounding each cover 6 there may be provided a metallic shield in the form of a tape or braid,

adapted to reduce electrostatic stresses and to provide a safe and continuous ground connection.

The several juxtaposed insulated conductors are cabled together, for example, in the form of a 3-conductor cable shown in the drawing. In the event that additional ground capacity is required, a plurality of grounded conductors ID are assembled in the valleys or interstices formed between the adjacent conductors, as shown.

Figure 2 illustrates a step in the method of production wherein a plurality of juxtaposed electric conductors carrying metallic shielding have been arranged with the ground conductors H) in electrical contact therewith and wherein the assemblage has been enclosed with a belt or sheathing of crepe material such as indicated at l2. In practice, it has been demonstrated that In the embodiment of the invention illusexcellent results are obtained" by the utilization of crepe paper for this sheath, since it has inerent characteristics which enable it to partake of considerable elongation without rupture. However, instead of using crepe paper. other material characterized by a corrugated surface endowing the same with bulky and elastic qualities, may be used with equally good results. The belt or sheath of corrugated or crepe material is slightly tensioned where it spans the valleys between adjacent conductors or between the conductors and ground conductors in those cases where ground conductors are used. The crepe sheath as shown in Figures 1 and 2 constitutes a helical wrapping; thus it is tensioned in the direction of its length across said valleys.

After application of the crepe, tape or corrugated fibrous material which is tensioned over the assemblage, a jacket M of rubber or equivalent insulating material is extruded,'molded, or otherwise placed over the assemblage. Thereupon the assemblage is vulcanized. The vulcanizing step develops a pressure which forces the body or rubber insulation inwardly against the crepe sheath. Because of its inherent characteristics, this crepe sheath stretches to such an extent that it is forced inwardly into the valleys between the conductors or between the ground wires I and the adjacent conductors, as shown in section in Figure 3. Thus the crepe material is made to conform closely to the contour of the assembled conductors and ground wires. Since the crepe paper or equivalent sheath is forced inwardly. into the valleys, the mass of insulated material I4 constituting the outer mass of insulation is also forced inwardly and thus eliminates the necessity of providing additional separate fillers such as were frequently required heretofore.

The novel cable describedhaving incorporated between the outer mass of insulation and the individual insulated conductors, the relatively bulky elasticcreped .layer provides an assemblage wherein the conductors are free to creep with relation to each other and in relation to the over-all body of insulation. This endows the assemblage with long life and great flexibility, and permits easy handling in service.

Conventional types of tape heretofore used, if used as a separating medium between conductors, will not possess the necessary characteristics.

under the pressure developed in vulcanization of the jacket, or will not permit the necessary fiow of rubber to properly fill the valleys between adjacent assembled conductors. On the other hand, when the crepe fibrous material is used in accordance with the teachings of the present invention, tests have shown that a complete filling of the valleys or interstices between adjacent conductors is obtained without rupture and at the same time the desirable freedom of relative movement of the conductors is obtained without sacrificing sturdiness or other necessary qualities. The crepe tape can be applied by conventional cabling or wrapping methods and by conventional types of machinery. Thus under the present invention an improved result is obtained without materially increasing the cost of production. It is also to be borne in mind that the crepe paper used'for the belting envelope is obtainable from stock sources of supply and hence its use does not materially increase production costs.

Wherever rubber or equivalent insulating material is referred to herein, I may utilize any thermo setting or thermoplastic material or syn- -thetic material having a rubber-like elastic nature.

While I have described quite precisely the embodiment of the invention illustrated and the specific steps in its methods of production, it is to be understood that the drawing and description are to be interpreted in an illustrative rather than in a limiting sense, since various tions holding parts of the crepe material in position in the valleys between said conductors, the said crepe material being tensioned in said valleys to an appreciable extent as a result of being forced inwardly by said outer body of insulating material substantially as described.

2. A cable for transmission of electric current consisting of a plurality of adjacent insulated conductors cabled together incontact with one another with valleys between them, a body of crepe paper enveloping the conductors and hav-' ing portions thereof distorted inwardly into the valleys, an outermost jacket of rubber having inwardly extended portions holding parts of the crepe paper-in said position in the valleys, the said crepe paper being characterized by an inherent ability to stretch an appreciable extent without rupture so that it may be forced inwardly into the valleys by said outer jacket of rubber substantially as described.

3. A cable for transmission of electric current "consisting of a plurality of adjacent insulated Practice has demonstrated that the i use of conventional tapes will either rupture conductors cabled together in contact with one another with valleys between them and enclosed with freedom for relative movement Within a body of rubber, a sheath of corrugated fibrous material tensioned around said insulated conductors and having portions projecting into the valleys between said conductors and held in tension in said valleys by respective portions of the rubber body which extend inwardly and partially occupy said valleys.

4; A cable for transmission of electric current consisting of a'plurality of adjacent insulated conductors cabled together in contact with valleys between them, a metallic shield enveloping each conductor, a metallicground strand contacting said shields, a sheath ofrcrepe paper tensioned around and enclosing said shield, said conductors a sheath of corrugated fibrous material characterized by an inherent ability to stretch an appreciableextent without rupture, enclosing all the described components in a body of vulcanizthus force the saidcrepe paper sheath inwardly into the valleys between said conductors.

7. In the manufacture of cables for the transmission of electric current, the method which comprises cabling together a plurality of insulated conductors, helicaily tensioning a tape of crepe paper around the cabled conductors, extruding a mass of rubber into direct contact with said sheath to thus envelop the same, and vulcanizing said rubber mass, thus forcing the sheath of crepe material radially inward into the valleys between said conductors.

' JAMES J. MORRISON. 

